Reamers are typically employed for enlarging boreholes in subterranean formations. In drilling oil, gas, and geothermal wells, casing is usually installed and cemented to, among other things, prevent the well bore walls from caving into the borehole while providing requisite shoring for subsequent drilling operation to achieve greater well depths. Casing is also installed to isolate different formations, to prevent cross flow of formation fluids, and to enable control of formation fluids and pressure as the borehole is drilled. To increase the depth of a previously drilled borehole, new casing, or liner is extended below the initial casing. The diameter of any subsequent sections of the well may be reduced because the drill bit and any further casing or liner must pass through the interior of the initial casing. Such reductions in the borehole diameter may limit the production flow rate of oil and gas through the borehole. Accordingly, a borehole may be enlarged in diameter below the initial casing to a diameter greater than an outer diameter of the initial casing prior to installing additional casing or liner to minimize any reduction in interior diameter of a production-ready (i.e., cased or lined and cemented) borehole and enable better production flow rates of hydrocarbons through the borehole.
One conventional approach used to enlarge a subterranean borehole includes the use of an expandable reamer, alone or above a pilot bit sized to pass through the initial casing. Expandable reamers may include blades carrying cutting elements and that are pivotably or slidingly affixed to a tubular body and actuated between a retracted position and an expanded position. Another conventional approach used to enlarge a subterranean borehole includes employing a bottom-hole assembly comprising a fixed blade reamer, commonly termed a “reamer wing,” alone or above a pilot drill bit. The reamer may include a number of blades of differing radial extent to enable the reamer to pass eccentrically through the initial casing and subsequently, when the reamer is rotated about a central axis, enlarge the borehole below the initial casing.
In both approaches, superabrasive cutting elements such as those comprising polycrystalline diamond compacts (PDCs) may be used to engage and degrade the formation. Such cutting elements, when employed on the gage of a reamer blade, may require machining, such as grinding, after the cutting elements are affixed to a reamer blade to establish a cutting diameter of the reamer, to create a smooth wall of the borehole after the borehole is enlarged by other, more distal (with regard to the extent of the borehole) superabrasive cutting elements, and to reduce reactive torque on the reamer due to contact of the gage cutting elements with the borehole wall. For example, a linear edge may be ground into a side of a superabrasive table of an otherwise cylindrical cutting element. Such machining may require an additional step in production, and thus may increase the time and cost associated with manufacturing a reaming tool. Furthermore, superabrasive cutting elements, such as those comprising PDCs, exhibit internal residual compressive and tensile stresses attributable to the high pressure, high temperature process employed to form the PDC, to attach the PDC to a supporting substrate, or both, particularly, for example, at an interface between a polycrystalline diamond table of a PDC and a supporting tungsten carbide substrate. Machining can alter the magnitude and type of stresses resident in the as-formed PDC as well as symmetrical residual stress distribution, potentially compromising the integrity of the cutting superabrasive element, leading to early failure by mechanisms such as spalling or delamination of the PDC from the supporting substrate.